1. Field of the Invention
The present invention pertains to a method of quantitative isolation of representative saturate, aromatic and polar fractions from hydrocarbon oils by preparative scale supercritical fluid chromatography.
2. Background
Several methods exist for analysis of hydrocarbon oils, that is petroleum products which are generally characterized as gas oils, diesel fuels and turbine fuels. Mass spectrometry is widely used, for example, to determine the major fractions generally referred to as saturates, aromatics and polars. These fraction or component names are descriptive of the chemical structure of the hydrocarbons which comprise each of the fractions. The precision and accuracy of the fractionation step is critical to the precision, accuracy and utility of mass spectrometric analysis. Conventional practice requires the separation of the hydrocarbon "oil" or petroleum fuel into the three major components using a technique known as low-pressure liquid chromatography. ASTM Standard Test Method D2007 and ASTM Standard Test Method D2549 are examples of conventional techniques.
Both of the above-mentioned methods use glass columns packed with polar adsorbents such as silica gel, bauxite and clay which are packed by hand for each sample to be analyzed. Column packing is a variable which can have a major impact on the quality of the results of this procedure. Moreover, operator exposure to dust from the packing material is a potential health hazard. The petroleum liquid fractions are separated by successive elution of the column with different organic solvents. This separation technique is time-consuming, labor-intensive, requires significant judgment by the analyst and exposes the analyst to hazardous materials.
A technique known as analytical scale supercritical fluid chromatography is now proposed for use in the petroleum industry according to ASTM Standard Test Method D5186, for example. This technique relies on the use of an on-line detector, such as a flame ionization type detector, which destroys the samples of the separated fractions. Moreover, the sample sizes for analytical scale supercritical fluid chromatography are exceedingly small.
However, the present invention provides a method for determining the major fractions of hydrocarbon oils such as gas oils, diesel fuels, turbine fuels and similar petroleum fuels using a technique which overcomes several disadvantages of the prior art methods including those mentioned hereinabove.